Patent Literature 1 discloses a technique relating to a flexible flat cable (hereinafter abbreviated as an “FFC”).
In an electronic device in which two circuit boards are electrically connected to each other by an FFC, a differential data transmission scheme may be used in a case where signals of a great information volume, such as video signals, are transmitted.
One representative scheme belonging to the differential data transmission scheme is the LVDS (Low Voltage Differential Signaling). The LVDS is a technique that realizes high-speed digital interface, and used, for example, in a case where video signals are transmitted between circuit boards in a display apparatus. The transmission rate of the LVDS is several hundred Mbps per channel.
In recent years, display panels of higher resolution are available. For example, there is a display panel having about 4000×2000 pixels (hereinafter referred to as a “4k2k panel”). With a display apparatus having such a high-resolution display panel, the information volume of an image is greater than with a conventional display apparatus, and therefore the transmission volume of video signals becomes greater than with the conventional display apparatus. Accordingly, with such a display apparatus, even when the LVDS is used for transmitting video signals, it is difficult to suppress an increase in the number of signals (i.e., the number of channels) required to be transmitted. Then, when the number of signal lines (i.e., the number of channels) included in one FFC is increased in order to address the increase in the number of signals, various restrictions and difficulties may arise in designing circuit boards.
When the signal transmission volume per channel can be increased, the number of signal lines (i.e., the number of channels) included in one FFC can be reduced. Here, transmission schemes that realize the transmission volume per channel at gigabit rates (Gpbs) are proposed as techniques replacing the LVDS. The transmission schemes include, for example, the V-BY-One (registered trademark) HS providing the maximum transmission rate of 3.75 Gbps, and the eDP (embedded Display Port) providing the maximum transmission rate of 5.4 Gbps.
As a cable for transmitting high frequency signals based on such transmission schemes between circuit boards, generally, an FFC which is impedance-matched and capable of keeping the quality of the transmission signals is used. Such an FFC is generally structured as follows. A wiring conductor through which signals flow is covered by an insulator. On one surface (a shield surface) of the wiring conductor, a dielectric, a conductor metal foil for GND and an insulator are layered in order to prevent leakage or entry of electromagnetic noises. In the following, the one surface (the shield surface) of an FFC is referred to as the “shield surface of the FFC”, and the other surface thereof is referred to as the “signal surface of the FFC”.
With an electronic device having circuit boards connected to each other by the FFC, in some cases, when the signal surface of the FFC is brought into surface contact with a metal-made member (a metal material), a low-pass filter (LPF) may be formed by the capacitance occurring at the contact portion and the resistance component of the wire resistance and the like. This LPF may attenuate high frequency signals flowing through the FFC. This capacitance becomes greater in proportional to the contact area between the signal surface of the FFC and the metal material. As the capacitance is greater, the attenuation amount of the high frequency signals flowing through the FFC tends to increase.
For example, with a display apparatus including a liquid crystal panel as a display panel, circuit boards are generally disposed on a metal material (a supporter that supports the display unit of the liquid crystal panel) covering the back surface side of the liquid crystal panel. In order to prevent leakage or entry of electromagnetic noises, an FFC is disposed such that the shield surface is opposed to the rear cover of the display apparatus. Accordingly, when a “sag” or the like occurs at the FFC, the signal surface of the FFC may be brought into surface contact with the metal material.
Then, with an electronic device in which high frequency signals are transmitted and received between internal circuit boards at gigabit rates, when the metal material and the signal surface of an FFC are brought into surface contact with each other, the signals transmitted through the FFC attenuate, and the circuit board on the reception side may not be able to normally receive the signals.